Flying Dog Brewery in Frederick, Md., drew inspiration from south of the border for the latest entry in its Brewhouse Rarities series of limited releases. Agave Cerveza is a Mexican-style lager in the Corona or Tecate mold but with a little something extra. Head brewer Ben Clark incorporated agave nectar near the end of the boil for a honeylike richness and added a dash of lime juice post-fermentation for a tart, fruity finish. Pour it into a frosted glass, add a slice of citrus, and you could imagine you’re sipping a margarita.

If you let the beer warm up, though, you’ll detect a sweet, sticky, cereal flavor, as if you’ve bitten into a tortilla. That comes from what might be its most unusual ingredient, craft beer-wise: the flaked corn that makes up 30 percent of the grist.

Corn, in brewing parlance, is an adjunct, a barley substitute. It has also been a four-letter word, literally and figuratively, for a generation of craft beer enthusiasts who viewed it as a cut-rate filler used by large national and international breweries to make cheap, bland beer. Corn sugar, or dextrose, is highly fermentable and is used to boost the alcohol of malt liquors, beverages that have been implicated in a number of social ills. That hasn’t been an image polisher, either.

Corn wasn’t always such a villain.

Nineteenth-century lager brewers who emigrated to America found the barley here to be different from the Old World strains they were used to: It had six rows of grain on each ear rather than the customary two. That hardier variety contained more protein and less fermentable material, and it produced a beer with a rougher, huskier taste. Those pioneer brewers found, however, that by blending the barley with maize they could make a brew that was paler, clearer and smoother on the palate, an ideal thirst quencher for the sultrier North American summers. (Some brewers, like Anheuser-Busch with its vaunted Budweiser brand, used rice for the same purpose.)

Over the years the percentage of adjuncts in beer increased, particularly during World War II, when rationing forced brewers to scramble for any kind of fermentable they could find. “Beer and Brewing in America,” a slim 1949 volume published by the United States Brewers Foundation, estimated that the average barrel of American beer contained 44 pounds of farm products. Barley accounted for 29 pounds; the remaining one-third consisted of eight pounds of corn and smaller portions of rice, assorted grains, sugar and syrup.

The earliest craft brewers drew inspiration from the German Reinheitsgebot, or purity law, which stipulated that only barley malt could be used as a fermentable. “Craft beer was all about bringing more flavor into beer,” notes Jim Koch, chairman of Boston Beer. “We all looked down our nose at using adjuncts to lighten the beer. But it was never about what’s good and bad; it was about who we are and who we aren’t.” Koch admits to having used dextrose to prime his home brew when he was learning the ropes. But in his 30 years of professional brewing, he can’t recall using corn in any of his recipes.

Some of Koch’s smaller brethren have dabbled in corn. Twice a year, Jason Oliver of Devils Backbone Brewing brews a beer called 1949 Heartland Lager for his Roseland, Va., brewpub. It’s an attempt to duplicate that 1949 average as accurately as possible, using flaked corn, rice, wheat and both corn and cane sugars.

“Coors fans love this beer, which is funny because it has a bit more hop bitterness than our regular all-malt lager,” says Oliver. Like all of his beers, it’s served unpasteurized. Oliver says flash-heating does more to destroy flavor in light lagers than corn does.

The most recent batch of Heartland is gone, but Oliver has rotated in Hazy Summer, a brew he calls “an English farmhouse ale.” He tosses in a bit of flaked corn to lighten the body, plus unmalted wheat, coriander, lemon zest and rooibos tea.

Oliver is unapologetic about his choice of ingredients. “Belgians use sugar — cane, beet, candy and corn — and no one bitches at them,” he says. “I use ingredients for particular reasons, and nothing is off the table for me.”

Brewing with corn is more, not less, challenging, asserts Flying Dog’s Clark: “It produces such a clean, light-flavored brew that any sign of imperfection shines through.” He had to control the mash temperature precisely to prevent too much of the starch from being converted to fermentable sugars. It’s a tribute to his skill that he was able to lasso the alcohol content at a gentle 4.3 percent by volume.

“I have no qualms about what I’m doing,” Clark says of brewing with corn. “Some of the macro guys make a product that’s exceptional for what they’re doing.”

The Brewers Association, the trade group representing America’s small brewers, has never minded small-scale experimentation. But too much corn once could get you excluded from the fraternity. To qualify as a “craft brewer,” a beermaker has to be “traditional.” That term originally was defined as having either “an all-malt flagship” or “at least 50 percent of its volume in either all malt beers or in beers which use adjuncts to enhance rather than lighten flavor.” Wheat, rye, pumpkins, chili peppers and raspberries were okay; corn and rice were not.

In February, however, the association decided that its definition was overly restrictive in that it excluded old, family-owned brewers like August Schell and Yuengling. Those companies have been making flavorful beers since the 1800s but incorporate a small percentage of corn grits into their recipes. The BA’s new definition of “traditional” merely requires a brewer to have “a majority of its total beverage alcohol volume in beers whose flavor derives from traditional or innovative brewing ingredients.” No specific ingredient is verboten, although the revised definition does not consider flavored malt beverages like Four Loko or Joose to be beer.

(Craft breweries still have to be independent and small, producing fewer than 6 million barrels a year. But even Yuengling, which will vault over Boston Beer as the country’s largest craft brewer the next time statistics are compiled, easily qualifies, having brewed about 2.7 million barrels last year.)

“We wanted to get away from ‘this beer is better than that beer,’ ” says Paul Gatza, the BA's director. Noting that the guidelines define “craft brewer” rather than “craft beer,” he says: “It’s up to the drinker to decide what is a craft beer and what isn’t. Beauty is in the eye of the beer-holder.”